Process for making white clouded enamel



Patented Dec. 30, 1941 PROCESS FOR'MAKING WHITE CLOUDED ENAMEL IgnazKreidl, New York, N. Y. No Drawing. Original application August 21,

1936, Serial No. 97,286. Divided and this application January 29, 1941,Serial No. 376,473. In Austria September 25, 1935 6 Claims. (01. 106-49) This application is a divisional application of application SerialNumber 97,286, filed August 21, 1936.

This invention relates to a process for making white clouded enamel,more particularly iron enamel, by gas clouding, the white clouding beingbrought about by development of small gas bubbles from substances whichdecompose at the burning-in temperature, which substances are added tothe enamel composition on the mill instead of the usual solid whiteclouding agents.

The present invention depends upon the discovery that by means ofcertain metal oxides or compounds thereof, such as more particularlyoxides of iron, antimony, cerium, uranium, ar-

senic or mixtures containing these oxides, the

whiteness value of the gas clouding can be very considerably enhanced,whence a decolourising effect may be allied to gas clouding means whichhave a colouring efiect (for example may give rise to the formation ofsubstances having a colouring action, such as carbon compounds having acolouring efiect), obviously in consequence of the better burningbrought about by their oxidising effect at the burning-in temperature.

The process according to the invention consists in this that metaloxides, such as antimony oxide, uranium oxide, cerium oxide, ironoxide,arsenic oxide, or compounds of these oxides with other metal oxides, areintroduced into the enamel independently of the fact whether thecompound added as gas clouding agent contains one of these oxides ornot, the introduction of these oxides into the enamel however being madein such small quantities that in the enamel the oxide is contained onlyin a quantity such that any clouding that may be attributable to theoxide itself is without influence, but nevertheless in a quantitysufiicient for the oxide to enhance ing-in temperature, are added to theenamel on the mill in quantities which are so small that the solidresidue can bring about no clouding efiects, whilst on the other handthe volatile portion sufiices owing to the development of small gasbubbles to impart a white clouding asa result of these bubbles.

In these known processes the quantity of metal 'oxide for example standsin a definite ratio to the quantity of gas clouding agent or of thedecomposable portion which is active as gas clouding'agent and thequantity to be added as clouding agent depends on the quantity of the.gas

clouding agent introduced with the oxide, as a result of which a correctadjustment to the whiteness value of the enamel, at which the presentinvention aims, is not possible. In these known. processes the effectmay arise that either too little metal'oxide is introduced into theenamel with correct addition of clouding agent,'or

too much clouding agent must be added with cor-" rect addition of metaloxide.

In the process according to the present invention the action of theseoxides and compounds is an action which is quite difierent in naturefrom that of a clouding action. The action of these oxides appearsirrespective of whether these oxides or compounds are added to theenamel on the mill or are fused with the raw substances forming theenamel. The action also already appears with such small quantities thatany clouding effect attributable to these oxides themselves can beignored. How different this action is from a clouding action is apparentfrom the fact that oxides which are not capable of elfecting a cloudingat all, such as for example iron oxide and uranium oxide, are just aswell suited for the process according to the invention as for exampleantimony oxide and the like.

The efiect at which the invention aims already appears with a content ofthe said oxides and compounds of these oxides in the enamel amounting tofar below 1%, an increase of this content above 1% bringing with it nofurther advantages as regards the action at which the invention aims.Preferably an addition is made in such a small quantity that,independently of the fact whether the compounds added as gas cloudingagent contain one of these oxides or not, the total quantity of theseoxides does not exceed 1%, and advantageously lies below 1%.

The action of these substances is obviously to be attributed to thisthat in the quantities in which they exert their effect in the processaccording to the invention they are without injurious auxiliary efiecton the slip or a constituent of the slip.

Not only however are the oxides of antimony, uranium, iron, cerium andarsenic, all of which are capable of forming several oxidation stages,suitable for carrying out the process according to the invention, thatis to say for introduction into the enamel, but also mixtures containingsuch oxides and also compounds of these oxides may be used, moreparticularly their compounds with other oxides, e. g. antimoniates orthe like.

The process according to the invention is particularly suitable forthose methods of making white clouded enamel in which gas cloudingagents are used in conjunction with enamel frits, which in the slippossess larger colloidal portions than normal enamel frits.- For examplethe colloidal properties or the colloidal portions of an enamel frit,that is to say the fritted raw mixture of the enamel charge, can beenhanced during normal grinding on normal enamel mills by variation ofthe composition of the enamel charge, for example by raising thefluorine content in normal enamel compositions. Normal enamelcompositions or charges contain approximately 5% fluorine with aproportion between alkali and boric acid of 1% parts alkali to one partboric acid. By raising the fluorine content to approximately double theamount, that is to say to about -12% fluorine for example, frits in acolloid-like state with a normal ratio of alkali to boric acid may beobtained, the fluorine however preferably being introduced in the formof alkali fluosilicate, such as for example sodium fluosilicate.

Examples 1 Grams Enamel mass 1 r 1,000 Water -1- l c 5,00 Methylene blue0.25 Cerium oxide" p w v r r 2 Clay V V 100 are ground up on the milland thereupon applied in the usual manner and burnt in.

2 Grams Enamel mass 1,000 Water 500 Methylene blue 0.25 Cerium fluoride5 Clay are ground up on the mill and thereupon applied in the usualmanner and burnt in.

In these examples a frit particularly suitable for gas cloudings, and infact a fluorine-rich frit of highly colloidal properties was used asenamel frit, in which the fluorine content originate from alkalifluorides or alkali silicofluorides. However, the invention of course isnot limited to such frits.

The additions forming the subject of the invention may be added to theenamel frit or to the enamel slip not only on the mill but also readypreviously to-a constituent of the enamel slip, or may also be fusedtogether with the raw substances forming the enamel.

What I claim is:

1. In a method of producing a gas clouded viterous enamel, the step ofincorporating in the enamel batch a compound containing cerium in anamount less than 1% of the enamel.

2. A process as claimed in claim 1 in which said compound also containsoxygen.

3. In a process of producing a gas clouded viterous enamel from a frit,in which the frit is produced by melting together and grinding a mixtureof materials, the step of adding to the frit materials before melting acompound con-- taining cerium in an amount less than 1% of the enamel.

4. In a method of producing a gas clouded viterous enamel the step ofadding to the enamel slip a compound containing cerium in an amount lessthan 1% of the enamel.

5. An article of manufacture comprising a metal article having thereon acoating of gas clouded viterous enamel containing cerium in a quantityless than 1% of the enamel.

6. An article as claimed in claim 5 in which said compound also containsoxygen.

'IGNAZ KREIDL.

